On the use of a satellite remote-sensing-based approach for determining aerosol direct radiative effect over land: a case study over China

Abstract

Abstract.A satellite-based approach to derive the aerosol direct shortwave (SW) radiative effect (ADRE) was studied in an environment with highly variable aerosol conditions over eastern China from March to October 2009. The method is based on using coincident SW top-of-the-atmosphere (TOA) fluxes from the Clouds and the Earth's Radiant Energy System (CERES) and aerosol optical depths (AODs) from the MODerate Resolution Imaging Spectroradiometer (MODIS) to derive SW clear-sky ADRE. The estimate for the aerosolfree TOA flux (F 0,TOA ) is obtained by establishing linear regression between CERES SW TOA fluxes and MODIS AODs. A normalization procedure to a fixed solar zenith angle, Earth-Sun distance and atmospheric water vapor content was applied to the CERES fluxes prior to the linear fit against AOD to reduce the flux variation not related to aerosols. In the majority of the cases, the normalization increased positive correlation between observed SW TOA fluxes and AODs, and it decreased RMSE. The key question in the satellite-based approach is the accuracy of the estimated F 0,TOA . Comparison with simulated F 0,TOA showed that both the satellite method and the model produced qualitatively similar spatial patterns, but absolute values differed. In 58 % of the cases the satellite-based F 0,TOA was within ±10 W m −2 of the modeled value (about 7-8 % difference in flux values). Over bright surfaces, the satellite-based method tend to produce lower F 0,TOA than the model. The satellitebased clear-sky estimates for median instantaneous and diurnally averaged ADRE over the study area were −8.8 W m −2 and −5.1 W m −2 , respectively. Over heavily industrialized areas, the cooling at TOA was 2 to more than 3 times the median value, and associated with high AODs (> 0.5). Especially during the summer months, positive ADREs were observed locally over dark surfaces. This was most probably a method artifact related to systematic change of aerosol type, sub-visual cloud contamination or both.

Improving the Estimation of Daily Aerosol Optical Depth and Aerosol Radiative Effect Using an Optimized Artificial Neural Network

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Airborne Aerosol in Situ Measurements during TCAP: A Closure Study of Total Scattering

“…Although the importance of atmospheric aerosol in modifying the Earth's radiation budget has been recognized by many studies [1,2], the extent to which aerosol shapes the regional and global climate is still ambiguous [3,4]. The magnitude and sign of the aerosol-induced changes of the radiation budget at the regional and global scales are highly uncertain, since these changes are influenced substantially by strong temporal and spatial variations of aerosol loading, chemical composition and mixing state [5][6][7].…”

A novel methodology for large-scale daily assessment of the direct radiative forcing of smoke aerosols

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